The ankle joint is one of the most frequently used joints in the body, as it is required for any activity that involves walking or running. The ankle joint connects the lower leg and the foot of a person, providing a pivot point that allows the foot to rotate relative to the lower leg. Together the lower leg, ankle joint, and foot make up a complex system that must be sturdy yet flexible in order to bear a person's weight while providing freedom of movement.
During ambulation, and especially during strenuous sports such as football, basketball, tennis, or soccer, quick changes in direction or uneven playing surfaces can cause the ankle to move beyond its normal range of motion, resulting in a sprained ankle. A sprained ankle may be painful, and can make sports less enjoyable, reduce athletic performance, and adversely affect day to day activities. Further, once an ankle joint has been injured, the injury is more likely to recur. For these reasons, there has long been motivation to find ways to protect the ankle without restricting freedom of motion, to prevent injuries and to protect the ankle during recovery from a previous injury.
The ankle joint itself is comprised of a bone structure held together by ligaments. The bone structure of the ankle consists of seven tarsal bones, including the talus, calcaneus (heel bone), and navicular bones. The talus is the bone which lies adjacent to the lower ends of the tibia and fibula (the two lower leg bones).
A single triangular shaped ligament, the deltoid ligament, holds together the medial (inside) portion of the ankle joint, joining the tibia, talus, calcaneus, and navicular bones. Because of its size, the deltoid ligament is strong and relatively resistant to sprain injuries.
Four major ligaments, named for the bones they join together and their relative positions, hold together the lateral (outside) portion of the ankle joint. The anterior inferior tibiofibular ligament, located at the top of the ankle joint, joins the tibia and fibula. The anterior and posterior talofibular ligaments, located at the front and rear of the ankle joint respectively, join the talus and the fibula. The calcaneofibular ligament, located at the rear of the ankle joint, joins the calcaneus to the fibula. Most ankle sprains involve these ligaments on the lateral portion of the ankle joint.
The ligaments and bone structure which comprise the ankle joint determine the four basic ways that the foot can move relative to the lower leg. Dorsiflexion is when the toes are drawn toward the tibia (shin), as would occur when leaning forward. Plantar flexion is when the toes are pointed away from the tibia, as would occur when standing on tiptoes. Inversion is when the foot turns inwards, and eversion is when the foot rotates outwards.
Sprains may occur in any ligament in the ankle, but most sprains involve two particular ligaments on the outside of the ankle, the anterior talofibular ligament, and to a lesser extent, the calcaneofibular ligament. When an ankle sprain occurs, the anterior talofibular ligament is usually the first to be injured, followed by injury to the calcaneofibular ligament. For this reason, a sprained ankle usually involves injury to the anterior talofibular ligament or to both the anterior talofibular and the calcaneofibular ligaments, but a sprained ankle usually does not involve injury to the calcaneofibular ligament alone.
Many ankle sprains are the result of inversion, where the foot is rotated inward, which stretches the anterior talofibular ligament beyond its elastic limit. Injury to the anterior talofibular ligament is especially likely when the foot is plantar flexed and then undergoes forcible inversion. When the foot is at maximum plantar flexion, when the toes are pointed downward as far as possible, the anterior talofibular ligament is pulled taut. When the anterior talofibular ligament is taut, that ligament cannot stretch any further and any subsequent forcible inversion may cause that ligament to be strained, or partially or completely torn. Such forcible inversion might occur, for example, when an athlete jumps in the air and then lands on their own inverted foot or on an uneven surface, such as a hole, another player, or some other obstacle.
Ankle braces have been used for many years, in a variety of specific embodiments directed to particular applications, including protection of the anterior talofibular ligament. However, prior ankle braces designed to protect the anterior talofibular ligament have been made to fit either the right foot or the left foot, but not both. Thus, an ankle brace designed to protect the anterior talofibular ligament which could be worn on either the left or right foot would be desirable, to simplify inventory management and reduce costs.